Changes in prostaglandin synthesis and metabolism associated with labour, and the influence of dexamethasone, RU 486 and progesterone

Department of Obstetrics and Gynaecology, University of Glasgow, UK.

The objective was to compare the changes in prostaglandin synthesis and metabolism occurring within the fetal membranes that are associated with the onset of parturition and to study the effect of steroid hormones on prostaglandin metabolism. A tissue explant study was made of discs of amnion and chorion obtained from 24 pregnant women at 37-42 weeks' gestation following spontaneous labour and delivery (12 women) and elective caesarean section (12 women). Significantly more prostaglandin E2 (PGE2) and PGF2 alpha were synthesized by amnion obtained following spontaneous labour than elective caesarean section. Arachidonic acid stimulated both PGE2 and PGF2 alpha synthesis by amnion in both groups. Phorbol myristoyl acetate stimulated PGE2 synthesis in both groups. There was no difference between the groups in the capacity of the chorion to metabolize prostaglandins. Mifepristone (RU 486) reduced the metabolism of added PGE2 following spontaneous labour, while dexamethasone and progesterone had no effect on prostaglandin metabolism. In conclusion, the increase in concentration of PGE2 and PGF2 alpha associated with the onset of spontaneous labour is the result of an increase in synthesis rather than a reduction in metabolism. There was no decrease in metabolism to account for the increase in prostaglandin concentrations and, with the exception of mifepristone, metabolism was not altered by the addition of steroid hormones.

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